Virulence factors and antibiotic resistance determinants are distributed among Gram-negative bacteria by conjugative plasmids. All such plasmids express pili, filamentous structures which are essential for establishing the contact between donor and recipient cells necessary for DNA transfer. In the F conjugative system, more than fourteen genes in the F transfer operon appear to be involved in the synthesis and expression of F-pili. Many of these products have not been identified, and their molecular role is not yet understood. Recently we have shown that synthesis of F-pilus subunits requires the processing of F-traA product to F-pilin. The processing reaction requires an activity from a previously unidentified transfer operon gene (traQ), and may require additional unidentified activities as well. We plan to identify the genes and gene products involved in F-pilin subunit synthesis, and investigate the nature of the biochemical reactions which occur in this pathway. We also plan, with transducing phages and chimeric plasmid derivitives, to identify all of the genes and gene products which are involved in the assembly of F-pilin subunits, and to investigate their interactions with each other and with F-pilin during the assembly process. The studies proposed are expected to contribute to our understanding of pilus synthesis and expression, and to elucidate the role of pilus assembly and retraction in conjugation.